...In regards to the performance of a quarter wave, there is a lot of debate about that on the internet. The "Gold Standard" two meter antenna is the Larsen (Laird) NMO-150 5/8 wave. The 5/8 wave "in theory" has 3dB gain over the quarter wave which is about a half an S-unit difference. In actual practice, I've pulled over to the side of the road before and switched between a quarter wave and a 5/8 wave and have not been able to tell the difference. Additionally, when you are traveling at highway speeds the 5/8 wave, which is longer, will have considerable back-tilt which affects the performance as well...
I have an antenna switch in the car, and have driven down the road switching between a 5/8 wave and a
1/4 wave antenna. The difference is very slightly in favor of the 5/8 wave whip when signals are marginal,
but if I stop and measure them at any single location either might be better than the other. I really have to
keep switching back and forth between them as I drive to get a sense of which TENDS to be be a bit better
a little more often. The practical difference between them is very small, and only observable when signals
are marginal.
The main reason is that the theoretical 3dB gain of the 5/8 wave antenna depends on it being over an
infinite ground plane, and the roof of the average car or van is nowhere close to that on 2m. You'd need
at least 100' of ground plane in all directions around the antenna. Without that the 5/8 wave antenna
is at best an end-fed dipole with a 1/8 wave single wire feedline.
